1 . Field of the Invention
The present invention relates to a contact-type image sensor adapted for use in an image reading unit in an image reader, a facsimile machine, a copying machine or the like, and an information processing apparatus as mentioned above, utilizing said image sensor.
2. Related Background Art
FIG. 1A is a schematic lateral view of a contact-type image sensor, and FIG. 1B is a schematic lateral view showing a part of the image sensor in FIG. 1A, in a magnified manner.
In FIGS. 1A and 1B, there are shown a frame 151; an image reading glass 152; plate springs 153, 154; elastic members 155, 156; an optical system 157 such as a distributed refractive index lens; a sensor substrate 158; and a bottom plate 159.
As shown in FIGS. 1A and 1B, the image reading glass 152, constituting a transparent protective member, is supported on longitudinal ends thereof by the folded plate springs 153, 154 serving as lateral plates in such a manner that the image reading surface is pressed toward the frame 151 (direction indicated by an arrow aa). In order to avoid damage to glass 152 by said plate springs, elastic members 155, 156 such as rubber pieces are placed therebetween.
In the above-explained structure, however, there are often obtained different output signals from the same image, in the central and end portions thereof. This phenomenon is attributed principally to the unevenness in the illuminating light quantity, and has been resolved by shading correction or the like. However various experiments and investigations by the present inventors have revealed that certain cases cannot be satisfactorily resolved by shading correction alone.
More specifically, some of the problems arise from the mounting method of the image reading glass. Though said glass is pressed by the lateral plates at the ends, it becomes bent by contact at the rear side with a hollow part of the frame and tends to be lifted in the central part, whereby the flatness of said glass is sometimes deteriorated to reduce the focus margin.
Also, the above-explained structure, in which the lateral plates protrude above the reading face of said glass, is associated with drawbacks such that an original document wider than the frame length cannot be passed and that even an original document narrower than the frame length may engage with the protruding portion of the lateral plate, thus eventually resulting in a sheet jamming if said original document is skewed in movement.
Furthermore, the contact between the image reading glass and the frame is often unstable, and dirt such as paper powder may intrude into the gap between said glass and the frame, causing an undesirable influence on the image reading operation.